Inside a graffiti-free church hall in south London around 15 black youngsters sit on plastic chairs. The boys - attending the 'From Boyhood To Manhood' gang intervention project - listen as their teacher warns them of repeating past mistakes.

'Think with your head, and not with your heart,' said Uanu Seshmi, who runs the project. 'Don't roam around on these streets. Find something to do with your life. Ignore all the negativity around you. Don't just listen to rap songs - understand them. Many of them have bad messages. Don't take them as a moral compass.'

The teenagers listen to the warning each morning as they arrive at 8.30 for an hour of yoga. Most have not attended school for months and have been referred to the project by social services and families after becoming involved in drugs, violence and gangs.

'The most important thing we can do is instil a sense of discipline in the kids,' said Seshmi. 'In many cases, they are from families that are simply not working. The parents are not around. Added to that, you have a host of temptations around here - drugs, theft, gangs and violence.'

Last year, more than 5,000 offences in which both victim and perpetrator were under 18 were reported in the borough of Southwark. Children as young as eight were bullying, mugging and using drugs.

'Gang culture was poorly understood,' said Seshmi. 'There was little concept of intervening to bring the kids out of gangs. Either you were at school or you had abandoned it altogether. For the kids that fell between the gaps, there was no help at all. That's the void we try to fill. We try and teach them how to respect themselves.'

The rules at 'From Boyhood To Manhood' are simple. No swearing. No fighting. Chores, such as cleaning, decorating the hall, and packing away equipment, must be completed on time. Schoolwork is of paramount importance; the children learn basic crafts and music tuition is available. A points system operates where youngsters are rewarded for sticking to the regime. Failure to do so leads to punishments - in most cases, menial kitchen tasks.

The children initially struggle with the regime. After the loose life that dictates gang culture, they take reluctantly to timetables and regulations. And for many, Seshmi is the first person to ever discipline them.

'It takes a while to understand that we're supposed to be responsible people,' said Edmond, who has been attending the project for over a year. 'I was just hanging out with kids on the street. I knew I was doing wrong things, but I was fed up at school. The teachers didn't seem to care about me. I was starting to get into trouble and thought I could get away with it. When I started coming here, I had the same attitude. That doesn't last long, though.'

In the afternoon, the boys stage a play they have been writing. The 15-minute performance takes in teenage pregnancy, drug-taking and gun violence. The boys are visibly hesitant in acting out their parts but as they perform to a rap soundtrack, they warm to the theme.

'We use a lot of rap music in the teaching sessions,' said one worker. 'The kids idolise American rappers like Tupac Shakur and Nas so we try not to dismiss their heroes. Only, we dissect the lyrics. That way they realise that while some of the songs have positive messages, many of them depict lifestyles that could be very dangerous. The way rappers treat women, for example. These young men are now finding girlfriends. We don't want them treating the girls as sex objects.'

Some of the rehabilitation techniques employed by 'From Boyhood To Manhood' are controversial. Boys caught fighting inside the hall are asked to participate in a boxing match. They wear protective clothing and light gloves. One such event is scheduled for two weeks' time. 'We really let them go for it,' said Seshmi. 'As you'd expect, it's often a scrappy fight since the kids are too angry to be able to fight properly. Gradually, though, they just punch themselves out. Once that happens, they usually start to feel rather sheepish. They realise the mistake that they've made.'